The master boot record occupies the first sector on the hard disk and is responsible for initiating the Windows boot procedure. The master boot record contains the partition table for the disk as well as a small program called the master boot code, which is responsible for locating the active, or bootable, partition, in the partition table. Once this occurs, the partition boot sector takes over and begins loading Windows. If the master boot record is corrupt, the partition boot sector can’t do its job and Windows won’t boot.
If your master boot record has been corrupted, you can use the Recovery Console tool Fixmbr to fix it. First, boot the system with the Windows XP CD and access the Recovery Console
To use the Fixmbr tool, from the Recovery Console command prompt, type
Where [device_name] is the device pathname of the drive to which you want to write a new master boot record. For example, the device pathname format for a standard bootable drive C configuration would look like this: